This invention relates to an exchange connected to a control channel junction line for a switching network wherein a plurality of digital exchanges are interconnected by way of digital junction lines (leased lines).
Although the number of talking channels between exchanges of a switching network is not always very great, if speech compression is involved, the number of talking channels used by the exchanges is further reduced. Therefore, enhancement in efficiency of control channels for controlling talking channels is demanded.
FIG. 15 schematically shows a digital switching network. Referring to FIG. 15, the network (leased network) shown includes a plurality of exchanges (PBX) 3-3.
Referring now to FIG. 16, each exchange 3-3 includes a digital junction line trunk 101, a plurality of speech compression trunks (VCT) 6 for 16 Kbps serving as low rate information multiplexing trunks, a speech path (NW) 51, a plurality of (two in FIG. 16) subscriber circuits (LC) 52, a main controller (CC) 53, and a main storage apparatus (MM) 54. A plurality of terminals 55 are connected to the exchange 3-3.
The digital junction line trunk 101 adds a D channel to multiplexed low rate information transmitted thereto from any of the 16 Kbps speech compression trunks 6, decomposes frames of digital information from a digital junction line to extract F (frame) bits and data and decomposes such data to extract compressed speech information and D channel information.
To this end, referring now to FIG. 17, the digital junction line trunk 101 includes a control channel transmission/reception apparatus 104, a pair of time switches 11A and 11B, a pair of multiplexing apparatus 12A and 12B, a pair of demultiplexing apparatus 13A and 13B, a framing and deframing section 14, a driver 15, a receiver 16, a line processor 18 and a memory 19.
The control channel transmission/reception apparatus 104 processes a D (control) channel (refer to 3 in FIG. 18) of 64 Kbps. In particular, the control channel transmission/reception apparatus 104 outputs a D channel received from the line processor 18 at the rate of 64 Kbps in accordance with a timing of a clock signal. Further, when a D channel transmitted at the rate of 64 Kbps is received, the control channel transmission/reception apparatus 104 outputs such control information to the line processor 18.
Each of the time switches 11A and 11B replaces or re-arranges the positions of time slots of a signal on an input highway in accordance with time slot position change designation information from the line processor 18.
Each of the multiplexing apparatus 12A and 12B multiplexes a plurality of time slots into the signal highway. Each of the demultiplexing apparatus 13A and 13B demultiplexes digital information on the highway into individual time slots.
The deframing and framing section 14 decomposes, from each frame of digital information received by way of the receiver 16 and having bit information of 1.5 Megabits, into F bits at the top of the frame and the remaining data, and stores such data obtained by way of the receiver 16 once into a memory and outputs the data at the rate of 2 Mbps (megabits/ second) of the internal highway in the trunk 101.
Further, the deframing and framing section 14 adds F bits to the top of each of data successively transmitted thereto at the rate of 2 Mbps from the multiplexing apparatus 12A to compose a frame, constructs digital information from such frames thus composed and sends the digital information at 1.5 Mbps by way of the driver 15.
The line processor 18 controls the time switches 11A and 11B in accordance with an instruction of the main controller 53 and sends a designated D channel to the control channel transmission/reception apparatus 104. The line processor 18 can communicate with the main controller 53. The memory 19 serves as a storage apparatus for the line processor 18.
In the digital junction line trunk 101 of the construction described above, a multiplexed compressed speech signal from any of the 16 Kbps speech compression trunks 6 is transmitted at the rate of 2 Mbps to the demultiplexing apparatus 13A. The compressed speech signal of 2 Mbps is demultiplexed into data of the rate of 64 Kbps equal to that before multiplexing by the demultiplexing apparatus 13A (refer to 2 of FIG. 18). Then, the time slot positions of the thus demultiplexed data are replaced or re-arranged by the time switch 11A to which the data are outputted from the demultiplexing apparatus 13A.
Meanwhile, the control channel transmission/ reception apparatus 104 outputs D channel information transmitted thereto from the line processor 18 to the time switch 11A at the rate of 64 Kbps.
Also the D channel information (refer to 3 of FIG. 18) is processed by replacement of re-arrangement of the time slot positions thereof by the time switch 11A similarly to the compressed speech signal described above.
The data (compressed speech information) and the D channel information from the compressed speech signal for which replacement of the time slot positions has been performed by the time switch 11A are individually outputted to the multiplexing apparatus 12A.
Thus, the compressed speech information in a demultiplexed condition is multiplexed by the multiplexing apparatus 12A so that it may include the D channel information, and the thus multiplexed information is outputted at the rate of 2 Mbps to the deframing and framing section 14.
The deframing and framing section 14 having received the thus multiplexed data provides F bits to each frame of the data to construct digital information and outputs the digital information at the rate of 1.5 Mbps to the digital junction line.
Meanwhile, digital information of 1.5 Mbps transmitted from another digital junction line is received by way of the receiver 16 by the deframing and framing section 14, in which the digital information is decomposed into F bits and data for each frame while it remains in a multiplexed condition.
A plurality of multiplexed data (refer to 1 of FIG. 18) obtained in this manner and destined for the terminals 55 are sent at the rate of 2 Mbps to and demultiplexed by the demultiplexing apparatus 13B and outputted as a plurality of data of the rate of 64 Kbps from the demultiplexing apparatus 13B.
Thereafter, each of the thus demultiplexed data is processed by replacement of time slot positions by the time switch 11B. After completion of such replacement of the time slot positions, D channel information of the data is sent to the line processor 18 by way of the control channel transmission/reception apparatus 104 while the compressed speech information is sent to the multiplexing apparatus 12B.
The D channel information transmitted to the line processor 18 is further sent to the main controller 53. Meanwhile, the compressed speech information transmitted to the multiplexing apparatus 12B is multiplexed again by the multiplexing apparatus 12B. In other words, compressed speech information from which D channel information has been removed is multiplexed. Thereafter, the compressed speech information multiplexed by the multiplexing apparatus 12B is outputted to the channel 51.
By the way, the 16 Kbps speech compression trunk 6 of FIG. 16 mentioned hereinabove multiplexes compressed speech signals of low rate information transmitted thereto from the terminals 55 by way of the associated subscriber circuits 52 and the speech path 51.
In particular, the 16 Kbps speech compression trunk 6 compresses compressed speech signals supplied thereto from the terminals 55 side to 16 Kbps and outputs four such signals into a B channel.
Further, the 16 Kbps speech compression trunk 6 demultiplexes a speech compression signal from the B channel supplied thereto from the junction line side and distributes the compressed speech signals obtained by the demultiplexing to the terminals 55. It is to be noted that, while the 16 Kbps speech compression trunk 6 compresses a compressed speech signal into 16 Kbps, it may be replaced by another speech compression trunk for compressing a compressed speech signal into 32 Kbps (32 Kbps speech compression trunk).
The main controller 53 is a CPU (central processing unit) for performing management and control of the exchange, and the main storage apparatus 54 is a memory which is used when the main control controller 53 performs its management and control functions.
In the exchange 3-3 of the construction described above, compressed speech signals from the terminals 55 are multiplexed by one of the 16 Kbps speech compression trunks 6. Then, the multiplexed compressed speech signal is additionally provided with a D channel by the digital junction line trunk 101 and sent at the rate of 1.5 Mbps into the digital junction line.
In particular, as seen from FIG. 15, multiplexed data from any of the exchanges to a particular destination are distributed by the leased network to a particular one of the exchanges. It is to be noted that the multiplexed data illustrated at 1 of FIG. 18 corresponds to the multiplexed data illustrated at 1 of FIG. 15.
By the way, the exchange described above sometimes has such a modified construction that, as shown in FIG. 19, it includes a plurality of digital junction line trunks 101 some of which are provided with a time division multiplexing apparatus (TDM) 56.
However, such control channel junction line systems as described above have a subject to be solved in that the efficiency in use of channels is low since even a D channel which involves a small amount of information conforms to the CCITT standards and is transmitted at the rate of 64 Kbps similarly to a B channel.